Apparatus for treating water and/or wastewater which utilize conventional membrane separation technology incorporating reverse osmosis and/or nano-filtration thin film membrane separation technology are well known and have been commercially available for many years. One example of an apparatus utilizing conventional membrane separation technology is shown in FIG. 1, defined hereafter, and outlined in general terms below.
Conventional membrane separation technology generally incorporates the following processes.
A raw (untreated) water source A is directed to the inlet of the conventional membrane separation device in either a flooded suction condition or under pressure by either a raw feed booster pump or via gravity feed.
A coarse filter B is placed prior to the conventional membrane separation device to separate large solids that might interfere with or damage subsequent pumps and/or membranes.
Pre-treatment apparatus C and devices are then placed to remove dissolved ions, polar contaminates and/or suspended contaminates that might cause damage to, or prevent the efficient operation of, the membrane separator. A partial list of common devices now used with conventional membrane separation technology, chemicals used, costs associated with the pre-treatment devices and the contaminates that they are designed to remove is shown below.
DEVICE CHEMICALS USED COSTS CONTAMINATES REMOVED MANGANESE GREENS POTASSIUM PERMANGANATE MEDIA REPLACEMENT, IRON, MANGANESE AND IRON FILTERS MECHANICAL UP-KEEP CHEMICAL FEEDS WATER WASTAGE ACIDIFICATION HYDROCHLORIC ACID, ACID FEED NONE, ALLOWS OPERATION SULPHURIC ACID, MECHANICAL UPKEEP ON HARD WATER PHOSPHORIC ACID CHLORINE/SAND CHLORINE COMPOUNDS MECHANICAL UP-KEEP, IRON, MANGANESE, FILTRATION IRON FILTERS MEDIA REPLACEMENT, BACTERIA, SOME CHEMICAL FEEDS ORGANICS WATER WASTAGE DECHLORINATION ACTIVATED CARBON, MEDIA REPLACEMENT, CHLORINE, OZONE, EQUIPMENT SODIUM THIOSULPHITE FEED CHEMICAL FEEDS, SOME ORGANICS WATER WASTAGE MECHANICAL UP-KEEP OZONATION DESICCANTS, OZONE DESICCANT UP-KEEP, IRON, MANGANESE, MECHANICAL UP-KEEP SOME ORGANICS, COLOR OZONE DESTRUCT SYSTEMS MEDIA SYSTEM MEDIA REPLACEMENT, OZONE MECHANICAL UP-KEEP SAND FILTERS NONE MEDIA REPLACEMENT, SUSPENDED SOLIDS, MECHANICAL UP-KEEP PARTICULATES, TURBIDITY WATER SOFTENER SODIUM CHLORIDE SALT, SALT FEED, CALCIUM, MAGNESIUM ION EXCHANGER POTASSIUM CHLORIDE SALT MEDIA REPLACEMENT, HARDNESS MECHANICAL UP-KEEP ORGANIC SCAVAGING SODIUM CHLORIDE SALT, SALT FEED, SOME ORGANICS, SOME ION EXCHANGER CAUSTIC SODA CAUSTIC FEED, FORMS OF SILICA, MEDIA REPLACEMENT, COLOR, SULPHATES MECHANICAL UP-KEEP SODA ASH/LIME SODA ASH, SODA ASH FEED, CALCIUM, MAGNESIUM EXCHANGE SOFTENERS SODIUM CARBONATE SODIUM CARBONATE FEED HARDNESS, SUSPENDED MECHANICAL UPKEEP SOLIDS, PARTICULATES, FILTER BED UPKEEP TURBIDITY MEDIA REPLACEMENT
Fine polishing filters D, generally of the disposable cartridge type, are provided with smaller systems and/or automated sand filter/coagulant systems are provided with larger systems and follow the pretreatment package. The purpose of this is to provide both filtration to below 15 microns and a silt density index (SDI) of below 5. These are the maximum levels normally acceptable with conventional membrane separation technologies.
A raw feed water shut-off valve E, usually automatic and controlled by the membrane separator device, is normally incorporated in order to prevent raw feed water from entering the membrane separator device when not in operation.
A raw feed water system pressure boost pump F or boost pump set is arranged following the shut-off valve to increase the pressure of the raw feed water to an acceptable level above the osmotic pressure of the raw feed water solution. Operating pressures vary from device to device. In general, the higher the total dissolved solids level of the raw feed water solution to be treated, the higher the operating pressure of the device. Common operating pressures are shown below.
 FEED SOLUTION TOTAL DISSOLVED TYPICAL OPERATING SOLIDS RANGE PRESSURE RANGE LOW SALINITY 0 to 1,000 mg/l 60 to 150 psi SLIGHTLY BRACKISH WATER 1,000 to 5,000 mg/l 150 to 250 psi MODERATELY BRACKISH 5,000 to 10,000 mg/l 250 to 550 psi HIGHLY BRACKISH WATER 10,000 to 25,000 mg/l 450 to 850 psi SEA WATER 25,000 to 38,000 mg/l 800 to 1,150 psi EXTREME SALINITY 35,000 to 50,000 mg/l 900 to 1,850 psi
As higher operating pressures improve both the product water output of membrane separators operated in the conventional manner and the product water quality, higher pressures than those indicated for the level of dissolved solids present in the raw feed water are sometimes used, but operating at higher pressures results in higher operating costs per volume of product water recovered.
The raw feed water system pressure boost pump or pump set must produce both the pressure required to operate the membrane separator and the required flow as well. Most conventional membrane separator specifications will only allow 10 to 15% recovery of the raw feed water stream if rated membrane service life, final water quality parameters and membrane warranty conditions are to be met. Some conventional membrane separator system designs do not follow these specifications, but this is bad practice.
Pump/motor combinations may include air-cooled motors with positive displacement pumps, single stage centrifugal pumps, or multi-stage centrifugal pumps, or water-cooled submersed motors with multi-staged centrifugal pumps. Average motor efficiencies for these pump designs are as follows.
 Air-Cooled Motor, Positive Displacement Pump 55% Air-Cooled Motor, Centrifugal Pump 60% Water Cooled, Submersed Motor, Centrifugal Pump 75%
The majority of conventional membrane separator designs operate with air-cooled motors. These are the least efficient and heat generated by the motor is lost to the atmosphere.
In order to meet the membrane separator warranty specifications, the system pressure booster pump/pump set must be capable of producing no less than 8, but preferably 10, times the anticipated flow of final recovered product water. The excess water may be discharged, creating a very water wasteful situation, or be partially recycled. In either case, the raw feed water main drive pump(s) must be capable of pressurizing the same volume of water. This involves considerable horsepower as shown below.
 FULL NO RECIRCULATION RECIRCULATION CONDITION: SEA WATER, SEA WATER, 30,000 TDS 30,000 TDS OPERATION PRESSURE: 850 PSI 850 PSI REQUIRED PRODUCT 1 USGPM 1 USGPM WATER FLOW: REQUIRED MEMBRANE 10 USGPM 10 USGPM TOTAL: FEED FLOW TOTAL MAIN DRIVE 10 USGPM 10 USGPM PUMP FLOW RECIRCULATION FLOW: 8 USGPM 0 USGPM WASTE FLOW: 1 USGPM 9 USGPM HORSEPOWER FORMULA: ##EQU1##
Therefore, under the above conditions, the horsepower requirements of a membrane separator operating in a conventional manner with an air-cooled motor and centrifugal pump would be: ##EQU2##
A Membrane Housing G accepts the flow from the raw feed water system pressure booster pump. The typical membrane housing feeds one or more membrane separators H, placed in series, within the housing with raw water from one end only, and in one direction only. The raw feed water is fed directly at the end of the membrane separator placed first within the housing. Brine seals (generally of a "U"-cup design) are placed on each membrane separator element within a series feed housing set, generally at the feed end. The brine seals prevent the flow of raw feed water around the membrane separator and force the water through the membrane separator feed spacers. This causes a jetting effect against the feed side of the membrane, potentially causing premature membrane wear and channeling.
Waste water is discharged from the membrane feed spacers at the end of the membrane separator opposite the feed end. The membrane separator arranged last in the series receives more concentrated feed water since the membrane separators arranged earlier in the series extract water from the feed water solution. This increases the concentration of contaminants in the feed water as it passes through each separator which in turn causes premature wear on the membranes placed last in series. This problem is further exacerbated if a membrane separator design incorporates an array lay-out.
The membrane separators are periodically flushed to remove particulates, solids and sludge present in the feed spacers within the membrane separators. When flushing multiple membrane separators arranged in series, flushing occurs in the same direction as operational flow. This minimizes the effectiveness of the flushing operation, particularly the flushing of the middle and final membrane separators since particulates, solids and sludge present in the feed spacers of earlier membrane separators are forced into the feed spacers of subsequent membrane separators. Flushing also cannot remove solids, sludges or other materials that may coat the membrane surface. This is particularly a problem if the membrane separator design incorporates an array lay-out.
Membrane selection is dependent upon the raw feed water conditions and final product water quality and quantity desired. All conventional membrane separators incorporate either diamond feed spacers or parallel feed spacers. These conventional feed spacers create a space between adjacent portions of the membrane and allow water to flow over the adjacent portions. Particulates passing along the feed spacers tend to get trapped causing plugging of the membrane separator.
The trapping of particulates within the feed spacers presents a recovery problem for conventional membrane separator designs. Recovery is the amount of water removed from the raw feed water. The resultant concentrated waste stream is the final volume of water remaining from the raw feed stream once the membrane separator has extracted a given product water volume. If, for example, 100 gallons of raw feed water enter the conventional membrane separator system and 50 gallons are removed as product water, 50 gallons of concentrated waste remains as the waste discharge stream. This equates to 50% recovery.
Ions present in the raw feed water are initially dissolved in solution, but as water is extracted from the raw feed water stream the volume of raw water remaining decreases. If the contaminating ions are too concentrated in the remaining volume (in excess of the Ksp of the solution), some will fall out of solution within the membrane feed spacer structure and will cause membrane fouling by coating the membrane separator thin-film surface itself or plugging of the membrane separator feed spacers, preventing that section of the membrane separator from producing product water. This may be especially dangerous in the case of conventional membrane separators if the contaminates leaving the dissolved state consist of iron, manganese, organics or oils. This problem is especially evident with array designs where high recoveries are attempted.
A membrane waste outlet pressure control valve I is utilized to control back-pressure against the membrane separator and to control the volume of waste discharge water leaving the conventional unit.
Often, in order to reduce the membrane separator water wastage, a recirculation valve J is incorporated. The recirculation valve directs a selected portion of the waste stream from the membrane separator, prior to its exiting through the membrane waste outlet/system pressure control valve, back to the raw feed water system pressure boost pump inlet. This water is retained within the system but must be repressurized to the system operating pressure before being returned to the membrane separators. Although this methodology reduces water wastage, no advantages are gained in power or horsepower reduction.
The returned water from the concentrate waste outlet that is recirculated will be higher in total dissolved solids than the incoming raw water and will contain concentrated levels of any contaminates present in the raw incoming water stream. This must be taken into account when determining the fouling characteristics of membrane separators operated in the conventional manner.
Most conventional membrane separator designs incorporate either an automated or manual membrane separator fast flush valve K. This valve allows raw water, or an external fresh water source, to be sent at full pump velocity through the membrane separator feed spacers to assist in dislodging materials that have been caught within the membrane separator feed spacers. Membrane separator flushing is in a single direction only and is not highly effective.
Optional membrane chemical feed tanks L are sometimes included as clean in place additions within the conventional membrane separator design to provide for chemical cleaning of the membrane separator(s) once they have become fouled or coated.
Chemical treatment M of the final recovered product water is often necessary with conventional membrane separation technologies, especially if acid feed strategies are utilized as part of the pre-treatment method. The final product water produced by conventional membrane separation technologies is, generally, very aggressive and unsuitable for most domestic purposes and distribution piping.
The currently available conventional membrane separator apparatus have many undesirable characteristics. Of these undesirable characteristics, the most undesirable are:
a) the low life expectancy of membrane separators operated in the conventional manner due to chemical cleaning requirements and pretreatment failures as well as normal wear; PA1 b) the accelerated wear of membrane separators placed last in series feed configurations due to higher total dissolved solids/contaminate loading as the feed solution becomes more concentrated from the membrane separators placed earlier in series extracting product water from the solution; PA1 c) the accelerated wear of the membrane separators from continuously experiencing solids and sludges re-introduced into the feed water with the recirculated concentrated waste from the membrane separators themselves, as this recirculated concentrated waste stream reenters the raw feed water booster pump and then directly re-enters the membrane separators; PA1 d) the accelerated wear of each first membrane separator placed within a series feed housing due to the jetting of the pressurized and high velocity feed water stream, which often contains abrasive solids from either the raw water stream itself or the recirculated water stream, directly against these first membrane separators placed in series; PA1 e) the accelerated wear and plugging of the membrane separators because the conventional membrane separator feed spacer design promotes retention and accumulation of solids, sludge and contaminates that fall out of solution due to super-saturation; PA1 f) the accelerated wear and plugging of conventional membrane separators from single direction flow, single direction and inefficient flushing of the feed spacers and thin-film surface; PA1 g) the high power requirements and operating costs associated with the conventional membrane separator device's raw feed water pressure booster pump and waste recovery/recirculation design; PA1 h) the significant manpower expenditures and associated operating costs relating to pre-treatment requirements of a membrane separator design operated in the conventional manner; PA1 i) the significant costs associated with pre-treatment chemicals and operation of pre-treatment equipment necessary with conventional membrane separator designs; PA1 j) the severe damage caused to membrane separators operated in the conventional manner when pre-treatment devices and/or chemical feed strategies fail; PA1 k) the damage caused to membrane separators operated in the conventional manner when raw feed water conditions change and cause the pre-treatment strategy to be no longer effective; PA1 l) the high costs associated with on-going up-grades of the pretreatment equipment/strategy as raw feed water conditions change; PA1 m) the potential poisoning of the final recovered product water if pre-treatment chemicals infiltrate the product stream due to membrane separator failure, membrane separator seal failure or membrane separator product core plug/seal failure; PA1 n) the significant chemical cleaning requirements necessary when operating membrane separation technology in the conventional manner in order to remove accumulated coating from the thin-film surface; PA1 o) the problems associated with disposal of the concentrated waste water from membrane separators operated with pre-treatment; and, PA1 p) the loss of membrane life expectancy and reduced membrane effectiveness each time a membrane separator is chemically cleaned in the conventional manner. One to five percent of the initial membrane separator output capability may be lost during each cleaning cycle. PA1 a water supply inlet; PA1 a treatment reactor having a housing, a membrane within the housing, a first port, a second port, and a third port in the housing, said treatment reactor being arranged such that a supply stream from the supply inlet fed to one of the first and second ports passes over the membrane to form a waste stream at the other of the first and second ports while consumption water passes through the membrane to the third port so that the waste stream contains an increased level of contaminants relative to the supply stream and the consumption stream; PA1 a storage tank for receiving and storing consumption water from the third port; PA1 a pump for pumping water through the reactor to said one of the first and second ports; PA1 ducting connecting the water supply inlet to the pump, the pump to the treatment reactor, and the treatment reactor to the storage tank and communicating a flow of water therebetween; PA1 and a valve for use in controlling flow of the water through the ducting; PA1 said valve comprising; PA1 a valve body; PA1 a plurality of ports in the valve body, each port having a channel extending into the valve body for communication of water thereto; PA1 a cylindrical bore arranged along an axis of the valve body such that each said channel extends through the valve body to the bore defining an opening at the bore; PA1 a valve member having a cylindrical outer surface arranged as a sliding fit within the bore and movable longitudinally in the valve body and arranged relative thereto so as to provide a plurality of longitudinally spaced positions for controlling water flow between selected ports; PA1 control means for selectably moving the valve member between the plurality of longitudinally spaced positions thereby controlling water flow through the ducting; PA1 an annular O-ring groove on the inner bore of the valve body for containing an O-ring for surrounding and sealing against the outer surface of the valve member; PA1 the O-ring groove having axially spaced side walls between which the O-ring is received, each side wall having a lip at the cylindrical bore extending axially from the side wall such that the space between the lips at the bore is less than the space between the side walls at a position spaced from the bore so as to act to retain the O-ring in the groove.
Some other disadvantages related to the use of conventional membrane separation technology are outlined below.
Operation of a conventional water treatment apparatus utilizing membrane separation technology has very high costs associated with it which often makes it economically unviable. These costs are due to the very high electrical operating costs, the very high costs and complicated operating procedures associated with substantial and complex pre-treatment equipment, and the very high costs associated with membrane separator element replacement when the membrane separators become fouled, plugged or prematurely damaged from inefficient flushing, necessary chemical cleaning procedures and/or over-all inefficient operation. In the event of pre-treatment failure, especially if high strength oxidants such as potassium permanganate, ozone or chlorine compounds are allowed to enter the membrane separator due to such a failure, total membrane destruction will often occur.
Membrane separators operated in the conventional manner together with necessary pre-treatment equipment and/or chemicals dictate that all feed water must be pre-treated. This entails the often excessive cost of treating the volume of water that is ultimately directed to final waste discharge as well as the volume of final recovered product water. In situations where the membrane separator is operating at fifty percent recovery, or less, pre-treatment devices and/or chemicals must be fed at more than twice the rate necessary for the actual usable product water produced, creating very high pre-treatment costs.
Pre-treatment presents a major disadvantage in final recovered product water quality. The most common forms of pre-treatment, such as water softeners and soda ash/lime softening, result in the exchange of monovalent ions (such as sodium, potassium and chloride) for the unacceptable ions that must be removed from the feed water of conventional membrane separator systems such as calcium, sulphate, magnesium, iron, manganese, silica, organic complexes, etc. Conventional membrane separators are very effective at removing calcium, sulphate, silica, etc., but less effective at removing sodium, chloride and potassium. If the raw feed water did not require pre-treatment, the resulting total dissolved solids levels and sodium, chloride and/or potassium levels of the final recovered product water would be lower.
Environmental disadvantages are numerous. Waste discharge streams must be disposed of. In many cases where membrane separation technology is applied in the conventional manner and pre-treatment devices and/or chemical feed pre-treatment strategies are applied, the waste discharge stream from the membrane separator may become toxic or hazardous. The sole reason for the toxicity or hazardous nature of the waste discharge stream may be due to the pre-treatment devices and pre-treatment chemical feeds themselves. Wastes produced during cleaning of membrane separators operated in the conventional manner are often toxic and, generally, never regarded as acceptable for discharge without special handling or treatment.
Membrane separators operated in the conventional manner are very water wasteful as frequent high volume raw water fast-flush cycles are necessary in order to help dislodge solids and sludge caught within the feed spacers and accumulated on the membrane separator thin-film surface. This presents both environmental concerns relating to the discharge of high volume waste streams and concerns over the depletion of the raw water supply.
Pre-treatment chemicals become concentrated in waste discharge streams from conventional membrane separator systems, often at levels above environmentally acceptable discharge standards. If pre-treatment chemicals were not necessary, the resulting waste discharge stream would be less problematic and more easily disposed of.
Safety disadvantages and concerns are also numerous with membrane separators, operated in the conventional manner, utilizing pre-treatment devices and/or chemical feed pre-treatment, especially when the intended use of the final recovered product water is for potable water purposes. The chemicals used as pre-treatment, such as potassium permanganate, many descalents, acid feeds and aluminum compounds are toxic and not acceptable for human consumption. In the event of a membrane breach, bypass or failure, these chemicals can enter and poison the final product water and any water stored in a product water reservoir.
Health disadvantages, especially with membrane separators operating in the conventional form for the purpose of producing potable water, can arise from the very aggressive nature of the final product water recovered. The final product water recovered typically exhibits a very low pH, very little buffering capacity, and little more than sodium and chloride as dissolved ions. This water will readily dissolve metals that it comes into contact with. This can be especially problematic in distribution systems and domestic residences where iron (from steel distribution piping), copper and brass (from both distribution piping and household plumbing) and even lead may be dissolved, rendering the water unsuitable for potable use.
One further health disadvantage with membrane separator technologies utilizing pre-treatment where the final recovered product water is intended for use as potable water is directly a result of the pre-treatment itself. Because the sodium levels of the raw water stream are elevated by most forms of pre-treatment and because sodium is amongst the most difficult ions for membrane separators to remove, the sodium levels of the final product water recovered is virtually always above the recommended potable water limit of 20 milligrams per liter (mg/l) or 20 parts per million (ppm) for those on sodium restricted diets and very often above the maximum recommended limit of 80 mg/l for the general population.
Nested valve sets used in conventional membrane separator designs present extreme disadvantages. Nested valve sets require high maintenance, present complex and considerable control problems, and are also very expensive. Failure of a valve within a nested valve set, or incorrect positioning for any reason including incorrect valve programming, can cause rapid and/or immediate failure of the membrane separator itself, failure of other system components, contaminated final recovered product water, and other severe problems.